GB684608A - Signalling system and signalling device - Google Patents

Abstract

684,608. Electric control systems. STAATSBEDRIJF DER POSTERIJEN TELEGRAFIE EN TELEFONIE. Oct. 28, 1949 [Oct. 28, 1948], No. 27738/49. Class 40 (i) [Also in Group XXXIX] In a signalling system in which dis crete signals are conveyed over a two wire. line to a register by the insertior of resistances in the line loop the sender comprises two groups of four resistance: each group being shunted by one of two oppositely poled rectifiers, each resistance corresponds to a digital value (in cluding zero) and a signal is sent by in serting in the loop one resistance of each group such that the numerical value o the digit to be sent is equal to the sum of the numerical values of the two resistances. The receiver first tests witt the line current in one direction to deter mine the value of the resistance of the first group and then with the current re versed to determine that of the seconc group, relays operated in the receiver as a result of these tests effecting registration of the digit in a binary code. Operation: Fig. 1. The sending station includes the resistances R'O, R'4, R'8, R<SP>1</SP>12 and R"0, R<SP>11</SP>1, R"2, R"3 each associated with a signalling contact which inserts it in circuit and each corresponding to the digital value indicated by its suffix. At the receiver resistances R1, R2 each of 15,000 ohms are connected to the a and b wires respectively. In the rest condition (relay O unoperated) the a wire is grounded and the b wire is connected to a 60 volt battery via R5 (5,000 ohms), and to obtain equal conditions of the signalling circuit when the current is reversed R3, R4 each of 15,000 ohms are connected to the a and b wires respectively. The voltage produced at the point A by the insertion of two signalling resistances is tested by means of an electronic potential-comparing device # referred to hereafter as the zero switch. The operation of # is such that if the voltage at A is less negative than that at B its contact remains in the position shown, but if the voltage at A becomes more negative than that of B the contact changes over at once (less than 1 msec.). The voltage at B is determined by a potentiometer (R6 to R10) under the control of the receiver relays, and normally (with only R6 and R7 in circuit) it is -19.4 volts. With a maximum line loop resistance (with the handset of a telephone at the sending station off its hook) of 2,000 ohms and with the maximum permissible leakance resistance a to b of 20,000 ohms the voltage at A is -19.2 volts. As soon as a signal is sent contact # changes over and operates start relay AX which locks up, extends battery to the first pair A-B of the receiving relays, and connects up R8 to change the voltage at B to -34.0 volts. The zero switch then determines if the voltage at A is less or more negative than -34 volts and relay B or A is operated as the case may be and locks up. The voltage at B is thus changed to - 27.75 volts or -40.5 volts respectively and the zero switch again determines whether the voltage at A is less or more negative than that at B, relay D or C operating as the case may be. Relay O comes up, reverses the current over the loop, switches the voltage at B back to.-34 volts, and brings up relay P to connect up receiving relays E-F. Resistances R"0. R"l, R"2, R"3 are equal respectively to R<SP>1</SP>0, R'4, R<SP>1</SP>8, R'12 and the second series of tests are conducted in like manner to the first series: At the end of the tests stop relay BX pulls up, locks under control of #, grounds the wires to the register relays, and brings up CX. All relays except BX, CX, O, and P then relapse. When the key at the sending station is released # restores its 'contact and during the release time of CX a circuit is completed to step the control switch to prepare for registration of the next signal. The arrangement provides for 16 different signals using 5 potential bands, but 12 may be signalled using 4 potential bands only. Construction of keyset. Three types of key board are described in each of which the depression of a key opens two signalling contacts and locks all the other keys. The first type (Fig. 5a) comprises two sets of four flat signalling bars (A-D and E-H) movable in two parallel planes in directions perpendicular to each other by depressing the keys. These bars carry pins (R, S) by which they are guided in a fixed frame. The lower ends of the keys are conical in form and round holes are provided in the bars offset with respect to the keys the arrangement being such that each key moves the two bars which intersect at its position. Locking bars W, X and Y, Z are provided in the spaces between the signalling bars and are moved by the pins on the latter when a key is depressed to prevent depression of a second key. The pins also serve to operate the signalling contacts. In the second type Fig. 6 (not shown), each set of four signalling bars is replaced by a square signalling plate, each plate being movable in any of the four directions under control of different keys; and in the third type each of these plates is replaced by two plates one moveable east and west and the other north and south. Specification 655,369 is referred to.